A wide variety of implantable medical devices are known and commercially available. Generally, implantable medical devices typically have a metal case and a connector block mounted to the metal case which includes receptacles for leads. Such leads may be used for electrical stimulation or for sensing of physiological activity or conditions. For example, an implantable cardiac device, e.g., a pacemaker, may use such leads to monitor activity of a human heart and also may additionally be used to perform therapy for the human heart. In other words, for example, heart activity may be monitored using the implantable device by sensing electrical signals generated by the heart, recording data indicative of the sensed electrical signals, and analyzing the recorded data to provide characterization data of the heart activity. Such implantable medical devices, e.g., such as those under the direction of a microprocessor, may generate data indicative of various conditions indicated by such heart activity and store data in memory.
It is generally desired, that data stored in implantable memory devices be provided to a physician or other personnel for collection and/or analysis. Further, due to various factors, such as the complexity of implantable medical devices; the need to diagnose, optimize and adjust various parameters during the implant procedure for such implantable medical devices; the occurrence of physiological changes; implantable device variables or drifts; and the need to retrieve data for analysis from the implantable medical device, extensive telemetry capabilities between implantable medical devices and external devices, e.g., an external programmer, are required. For example, the need to access system performance or trouble-shoot the patient, device, and/or lead system in an acute, clinical setting requires such telemetry capability between the implanted medical device and an external device.
Programmers used to adjust parameters of multi-function implantable medical devices typically include graphic displays, keyboards, or light pens for data entry and device control by operator manipulation, and also include printers or plotters to allow the user to easily control, evaluate, and document the extensive capabilities of the medical device. For example, such devices may include the Medtronic Model 9760 programmer.
Typically, a programmer used during a telemetry procedure is positioned remote from the patient. A programming head of the programmer, e.g., a wand or some other external device, containing at least an antenna, is connected to the remainder of the programmer via a stretchable coil cable and is positioned over the patient's implanted device site for programming or telemetry interrogation of the implanted device. The programmer typically consists of one or more microprocessors and contains programmable memory capable of storing executable programs under the control of the operator via a user interface. The implantable medical device may receive command instructions from the non-implanted external device, e.g., the programmer, which is external to the skin of the patient. Such command instructions are referred to herein as downlink transmissions, i.e., transmissions from the external device or programmer to the implantable medical device. For example, the received command instructions may include program instructions or steps for directing the operation of the implantable medical device. Further, for example, the received command instructions may also include data such as program limits and timing data.
Similarly, the implantable medical device may transmit data to the external device, e.g., programmer. Such transmissions are referred to herein as uplink transmissions, i.e., transmissions from the implantable medical device to the external device. In other words, the programmer may function to receive data from the implantable medical device as well as to transmit the commands thereto. Communication between the implanted device and the external device may be limited to transmissions by only one of the devices with the other device receiving those transmissions. Alternatively, communication between the implanted medical device and the external device may include transmissions by both devices.
The communication between the implanted medical device and the external device, e.g., programmer, is facilitated by receiving and transmitting circuitry included within the implanted medical device and the external device. The implanted medical device includes receiver and transmitter circuitry which may cooperate with other circuitry of the implanted medical device to receive information from the external device and to transmit data to the external device. Further, the external device includes analogous transmitting and receiving circuitry for communicating with the implanted medical device. Both the implanted medical device and the external device include antenna structures coupled to the receiver and transmitter circuitry for transmitting and receiving electromagnetic energy.
Various systems for performing telemetry with regard to implanted devices are known. For example, such systems are described in U.S. Pat. No. 5,127,404 issued to Wyborny, et al.; U.S. Pat. No. 4,556,063 issued to Thompson, et al.; and U.S. Pat. No. 5,342,408 issued to de Coriolis et al. Such conventional telemetry systems typically enclose the antenna or antennas of the implanted medical device inside the housing or case of the implantable device. As described above, such housings are typically metallic in nature and may be, for example, made of titanium or titanium alloys. Such metal housings may act as low pass filters to limit the bandwidth of signals transmitted from and received by the implanted medical devices. Conventional telemetry systems which enclose the antennas in the case generally have undesirably low transmission rates. Further, operation is forced to the lower frequency ranges due to the attenuation of higher frequencies by the case of the implanted device.
In such conventional telemetry systems, bandwidth is kept low to minimize the power consumed by the implanted medical device. Power consumption is a very important criteria in designing implantable medical devices. Such devices are typically powered by a depletable energy source, such as a battery. A depleted energy source requires replacement of the implanted device, which can be costly and is inconvenient.
Accordingly, there is a need to minimize power consumption by the implanted medical device. Various techniques of minimizing power consumption for telemetry functions have been described. For example, minimization of power consumption as described in U.S. Pat. No. 5,342,408 is accomplished by the intermittent use of receiving and transmitting circuitry of the implanted medical device to communicate with the programmer. In other words, transmitter and receiver circuitry are de-energized to reduce power consumption when such circuitry does not need to be activated. As such, there becomes a need to wake up the de-energized portions of the implanted medical device when desired to allow communication to occur. However, generally, a relatively large receiving antenna for the implanted medical device is required to couple sufficient electromagnetic energy to the receiving circuitry thereof to facilitate such a wake up function. Such an antenna is undesirable and inconsistent with a physically compact implanted medical device.
In addition to power reduction, another important design criterion for implanted medical devices is accurate communication of data between the external device and the implanted device. Downlink transmissions from the programmer to the implanted medical device must be received correctly. Similarly, uplink transmissions by the implanted medical device to the external device must be received correctly. This communication must occur in environments such as hospitals and doctors offices, which may be very noisy due to the presence of other electronic and electromagnetic sources. One aspect of assuring accuracy of transmitted data is establishing a reliable data link.
Generally, the external device's antenna is disposed in a moveable programmer head which is to be placed in close proximity to the implantation site of the implanted medical device to effect a reliable data link in conventional telemetry systems. Because the medical device is implanted and not visible, determining the proper orientation of the programming head of the external device can be difficult. To assure that the data is transmitted accurately, programming head antennas must be positioned to maximize signal strength received from the implanted medical device. As described in U.S. Pat. No. 5,342,408, a moveable programming head positioned external to the patient can include a signal strength indicator giving an indication of received signal strength to allow repositioning of the moveable programming head to maximize received signal strength. However, the physician handling the programming head has various tasks to perform and repositioning of the programming head to a particular position and maintaining such a position to maximize received signal strength is a task that makes completing the telemetry functions undesirably difficult.
Various references describe using the human body for communication functions. For example, U.S. Pat. No. 4,987,897 to Funke, entitled, "Body Bus Medical Device Communication System," describes using the human body as the communication transmission channel between two or more implantable modules and/or between at least one implantable module and an external skin electrode intended for connection to an external module. Further, U.S. Pat. No. 5,113,859 to Funke, entitled, "Acoustic Body Bus Medical Device Communication System," describes using the human body for ultrasonic coupling between two or more implantable modules and/or between at least one implantable module and an external skin transducer intended for connection to an external module. U.S. Pat. No. 5,796,827 to Coppersmith, et al., entitled, "System and Method For Near-Field Human-Body Coupling for Encrypted Communication with Identification Cards," describes a communication system wherein transmitter and receiver components of the communication system are capacitively coupled using the human body. Such communication systems using the human body for capacitive coupling are also described in an article entitled, "Personal Area Networks: Near-field intrabody communication," by T. G. Zimmerman, IBM Systems Journal, Vol. 35, Nos. 3 & 4 (1996) and in PCT International Publication No. WO 96/36134, entitled, "System For Non-Contact Sensing and Signaling Using Human Body as Signal Transmission Medium."
Further, U.S. Pat. No. 4,440,173 to Hudziak et al., entitled "Programmable Body Stimulation System" describes a stimulation system having a stimulation signal generator located within a housing for implantation in the body such that stimulation signals can be delivered by a lead to a desired body site. The lead used for delivering the stimulation signals is also allegedly used for receiving programming signals and delivering such signals to operating characteristic establishing circuitry of the system. This allegedly eliminates the need for an antenna coil within the housing for receiving such programming signals.
Table 1 below lists U.S. patents relating to communication techniques:
TABLE 1 ______________________________________ U.S. Pat. No. Inventor(s) Issue Date ______________________________________ 5,113,859 Funke 19 May 1992 5,678,202 Filimon, et al. 14 October 1997 4,440,160 Fischell, et al. 3 April 1984 4,471,786 Inagaki, et al. 18 September 1984 4,440,173 Hudziak, et al. 3 April 1984 4,481,950 Duggan 13 November 1984 4,886,064 Strandberg 12 December 1989 4,987,897 Funke 29 January 1991 5,312,446 Holscabach, et al. 17 May 1994 5,796,827 Coppersmith, et al. 18 August 1998 5,342,408 DeCoriolis, et al. 30 August 1994 ______________________________________
All references listed in Table 1, and elsewhere herein, are incorporated by reference in their respective entireties. As those of ordinary skill in the art will appreciate readily upon reading the Summary of the Invention, Detailed Description of the Embodiments, and claims set forth below, at least some of the devices and methods disclosed in the references of Table 1 and elsewhere herein may be modified advantageously by using the teachings of the present invention. However, the listing of any such references in Table 1, or elsewhere herein, is by no means an indication that such references are prior art to the present invention.